Generators of fluid wave trains

ABSTRACT

A generator produces vacuum or pressure surges in a sea or a lake so as to form seismic wave trains passing through the bottom of the water bed and back into the water for subsequent investigation. The generator includes a movable system, mainly a disc or a cylinder cover adapted to move between predetermined limits under the impact of a hammering means constituted as a piston urged forwardly in a cylinder so as to violently strike the rear end of the movable system and to produce thereby the desired surges to the rear and/or front of the movable system. The hammering means is subjected when released to the hydrostatic pressure which urges it forwardly into engagement with the rear end of the movable system constituted advantageously by a rod rigid with the disc or the like and extending coaxially in the cylinder for cooperation with the piston.

United States Patent 91 Muniz et a1.

GENERATORS OF FLUID WAVE TRAINS Inventors: Raymond Muniz, Versailles;Robert Argirakis, Legue de Longroi, both of France [73] Assignee:Compagnie Generale De Geophysique, Paris, France Filed: Jan. 23, 1969Appl. No.: 793,415

References Cited UNITED STATES PATENTS 10/1966 Bouyoucos 340/12 2/1968Schempf 181/5 June 26, 1973 Primary Examiner-Benjamin A. BorcheltAssistant Examiner-H. A. Birmiel Attorney-Waters, Roditi, SchwartzNissen [57] ABSTRACT A generator produces vacuum or pressure surges in asea or a lake so as to form seismic wave trains passing 7 through thebottom of the water bed and back into the water for subsequentinvestigation. The generator includes a movable system, mainly a disc ora cylinder cover adapted to move between predetermined limits under theimpact of a hammering means constituted as a piston urged forwardly in acylinder so as to violently strike the rear end of the movable systemand to produce thereby the desired surges to the rear and/or front ofthe movable system. The hammering means is subjected when released tothe hydrostatic pressure which urges it forwardly into engagement withthe rear end of the movable system constituted advantageously by a rodrigid with the disc or the like and extending coaxially in the cylinderfor cooperation with the piston.

7 Claims, 7 Drawing Figures A i a f 1 GENERATORS OF FLUID WAVE TRAINSThe present invention relates to a generator of fluid wave trains orshock waves adapted to be immersed in a body of water such as the sea, alake and the like and to produce wave trains constituted by surges offluid under increased or reduced pressure conditions and which may betermed respectively pressure and vacuum wave trains. Such generators arechiefly, but not exclusively intended for submarine seismic prospection.It is a well-known fact that submarine prospecting by seismic methods isnow increasing favor. According to said rnethods, seismic waves producedunder water arepropagated within the water and reach the bottom of thesea or of the lake so as to enter the underlying strata. After partialrefraction or reflection therein, they return to the water bed andre-enter the water in order to be finally collected by hydrophoneslocated at suitable points in or on the sea or lake.

The present invention is particularly directed to a generator of seismicwaves which may be utilized to in such a case.

It is known that wave trains resulting in seismic waves may be producedeither by a pressure surge caused'by a sudden increase in the volume ofan immersed object or by a vacuum or reduced pressure surge caused by avacuum developed suddenly within the water.

The generator according to the present invention is adapted forproducing wave trains of either type as re quired.

The problem to be solved consists in the production of a very high speedrelative movement between two members in order to produce the wave'train. According to the invention, this shifting of one member withreference to the other is obtained substantially by means of astationary member constituted by the outer surface of the generatorwhile the other member is constituted by a disc or cylinder cover whichis as light as possible and controlled by a rod entering the generator;a solid piston located in the generator strikes the end of the free endof said rod in each forward stroke so as to exert a hammering whichproduces, by reason of the light weight of the movable systemconstituted by the movable disc or cylinder and the associated controlrod, the desired wave train.

According to a further feature of the invention, the energy required fordisplacing piston is that of the hydrostatic pressure of the water inwhich the generator is immersed, said hydrostatic pressure beingcapable, by reason of a suitable size given to the piston, oftransmitting to the latter at the moment at which it is to strike themovable system a kinetic energy which is sufficient for producing aseismic wave of a suitable amplitude.

Of course, it is necessary when a wave train has been released to returnthe piston to its original starting position under the action of a forcewhich is large enough for it to overcome the hydrostatic pressure of thewater in which the generator is immersed. This operation is effected byauxiliary means which do not per se form part of the invention.

The great advantage ascribable to the use of the hydrostatic pressure ofwater for supplying kinetic energy to the generator piston resides inthat said hydrostatic pressure may produce the considerableinstantaneous power which is required for obtaining a high kineticenergy, whereas the power supplied by compressed gas,

for instance for returning the piston. into its starting position afterthe production of the wave train, may be much smaller since it ispossible to allow the return stroke of the piston to extend during aperiod which is much longer than that provided for its forward stroke.

According to a still further feature of the invention, the volume withinwhich the piston moves, once it has been brought into its startingposition, is subjected to a partial vacuum so as to-prevent the pressureof air from braking the forward thrust of the piston.

Further features and advantages of the invention will appear from thefollowing description, reference being made to the accompanyingdiagrammatic drawings wherein:

FIG. 1 illustrates an embodiment provided for the production both of apressure wave train and of a vacuum wave train, said embodimentincluding a movable system constituted by a simple disc; in saidembodiment the piston is returned into its starting position bycompressed gas;

FIGS. 2 to 5 illustrate partial views of different modifications of themovable system;

FIG. 6 illustrates an embodiment wherein the piston is returned to itsstarting position by hydraulic mean; and

FIG. 7 is a cross-section taken along line 27 in FIG.

The different generators illustrated in FIGS. 1 to S are illustrated ina horizontal position but, when used for submarine seismic prospectiozn,their axes extend vertically.

In H6. 1, the generator includes a cylinder 1 whose right-hand end 2 isprovided with a large opening 3 connection the right-hand chamberdefined by the piston 4 in the cylinder with the water in which thegenerator is immersed. The piston 4-is adapted to move in the cylinder 1and is urged towards the right-hand side a volume of compressed gasintroduced into the chamber 5 formed by the inside of the cylinderbetween the piston 4 and the corresponding end 6 on the left-hand side,said input of compressed gas being provided through the pipe 7. In theinitial position of the piston 4, it engages the right-hand end 2 of thecylinder 1. The piston 4 may be held in said initial starting positionby means of locking means illustrated diagrammatically by a catch 12preferably controlled electrically, said catch 12 being collapsible forreleasing the piston 4.

The movable system is constituted by a circular disc 8 carried by aspindle 9 extending through a central port formed in the end 6. The freeend of the spindle 9 is provided with a wear-resisting head 10 adaptedto be struck by the piston 4; The disc 8, when inoperative, engages theleft-hand end 6 of the cylinder and is urged into such a position by aspring 11 surrounding its spindle 9.

The operation of the apparatus is as follows: the compressed gas fed bythe pipe 7 urges the piston 4 towards its starting position to the rightagainst the action of the hydrostatic pressure exerted on the right-handside thereof. When the piston has reached its starting position, thepiston is locked by the catch 12, after which the piston being thus heldfast, the pressure of the gas in the cylinder chamber 5 to the left ofthe piston is diminished and a partial vacuum is preferably provided bymeans of suction exerted through the pipe 7. The wave train is thenobtained by :a mere release of the catch 12 so that when the catch hasactually retracted,

the hydrostatic-pressure exerted on the right-hand side of the piston 4urges the latter towardsthe left with a kinetic energy of the desiredvalue. The left'hand side of the piston 4 then strikes the head of thespindle 9 and produces a high speed shifting from right to left of thedisc 8 which is immersed in the water. Under the action of the vacuumthus formed between the righthand side of the disc 8 and the cover 6 ofthe cylinder, a vacuum train of waves arises while simultaneously apressure wave train is produced by the motion exerted by the leftsurface of said disc on the water. In order to accurately define themoment at which a wave train is produced, a contact-piece 13 is locatedsubstantially in transverse registry with the position occupied by thehead 10 when the disc is in its inoperative position. Said contact-piecewhen actuated by the forward movement of the piston defines the momentof initiation of a wave train. Similarly, the moment at which the piston4 starts on its forward travel is defined through actuation of a furthercontact-piece 14, which actuation starts operation of a recording means,whereas the moment defined on said recording means by the contact-piece13 corresponds, possibly after correction by a predetermined value, tothe generator of the wave train.

Of course, the contact-pieces l3 and 14 are drawn only symbolically inFIG. 1 and their detailed construction is irrelevent as concerns thepresent invention.

FIGS. 2 to S are partial view illustrating modifications of the movablesystem. The outer edge of the disc 8 illustrated in FIG. 2 is connectedwith the outer edge of the left-hand end 6 by an elastic diaphragmforming a bellows as illustrated at 15. Said elastic diaphragm preventsany external water from entering the space extending between the disc 8and the left-hand side of the end 6 during the movement of the disc fromthe right to the left whereby the surges forming the vacuum wave trainare eliminated so that withthe modification illustrated in FIG. 2 onlythe pressure wave train is obtained.

In the embodiment illustrated in FIG. 3, the disc 8 is rigid with anauxiliary cylinder 16 coaxially surrounding the cylinder 1'. A suitablepacking is inserted between the cylinders 1 and 16. In this embodiment,the vacuum wave train is again eliminated and only the pressure wavetrain remains.

In FIG. 4, the cylinder 1 includes an extension on the left-hand side,said extension forming a broader cylindrical section 18 rigid with thecylinder 1 and in which "the disc 10 is adapted to slide so as toproduce, as

above, a pure pressure wave train.

In the embodiment of FIG. 5, the disc 8 is rigid with a cylindricalsection 19 facing away from the cylinder 1 and slidingly fitted in anauxiliary stationary cylinder 20 rigidly connected with said cylinder 1by means which are not illustrated. A suitable packing is providedbetween the sliding cylindrical section 19 and the auxiliary cylinder 20which is closed at its outer end and inwardly subjected to a partialvacuum before the piston 4 is caused to move. It is apparent that withsuch an embodiment there is produced only a vacuum pressure wave byreason of the vacuum produced in the space between the two cylinders 1and 20 upon movement of the.disc towards the left away from the end 6 ofthe cylinder 1 while the pressure surges are eliminated by the closedcylinder 20.

Lastly, FIG. 6 illustrates a modification of the means for returningthepiston 4 to its staring position, said modification resorting tohydraulic control means. The. righthand end of the cylinder 1, itspiston 4 and stop catch 12 of FIG. 1 are illustrated in a manner similarto said FIG. 1 while the left-hand end of the cylinder 1 associated withthe movable system is not illustrated since it can be identical with anyof the arrangements illustrated in FIGS. 1 to 5.

In FIG. 6, the piston 4 instead of being free is secured to the end of acontrol rod 21 passing out of the cylinder 1 through the rear port 3whose diameter is much larger than that of said rod 21. The rod 21enters a further cylinder 22 coaxial with the cylinder 1 and rigidlysecured thereto in any suitable manner. A packing ensures fluidtightnessfor the rod 21 as it enters the cylinder 22. The .free end of the rod 21carries a head 23 while an auxiliary piston 24 is adapted to move in thecylinder 22, the outer end of which is closed. The auxiliary piston 24is provided with an axial bore in which the rod 21 is slidingly movable.The cylinder 22 is provided at its opposite ends with inputs for pipes25 and 26 through which oil or other suitable pressurized fluid can befed into or out of said cylinder 22 under the action of suitable controlmeans.

The operation is as follows:

The piston 4 being located at the inner end of its stroke after it hasstruck the movable system, oil under pressure enters through the pipe 25into the front chamber of the cylinder 22, while simultaneously the oilcarried in the rear chamber of said cylinder 22 passes out of it throughthe pipe 26. The oil pressure thus obtained urges forwardly theauxiliary piston 24 which was originally at the front end of its strokeso as to engage the head 23 of the rod 21 and to carry it along with thepiston 4 until the piston 4is locked in its rearrnost position by thecatch 12.

The piston-4 being thus locked in its starting position, the auxiliarypiston 24 is returned inwardly by the pressure of the oil drawn inthrough the pipe 26 while the oil underneath the auxiliary piston 24 isremoved through the pipe 25. The apparatus is thus ready for theexecution of a further operative stroke.

' FIG. 7 is a cross-section in a plane defined by the line 27 of FIG. 6,which plane is perpendicular to the axis of the cylinders l and 22. FIG.7 shows in combination with FIG. 6 the means for rigidly interconnectingthe two cylinders 1 and 21. As illustrated, three outer arms 28 arearranged in radial planes with reference to the cylinders and aresecured at their opposite ends to the corresponding cylinders. The arms28 are streamlined so as to offer minimum resistance against the waterflowing radially to either side of said arms before entering the annularopening 3 in the cylinder 1 during the operative stroke of the piston 4.

This manner of rigidly interconnecting two coaxial cylinders mayobviously be used in the case of the stationary cylinders oftheembodiment according to FIG.

It will be readily ascertained that many other embodiments of theinvention are possible within the scope of the accompanying claims.

What I claim is:

1. A generator of wave trains in water comprising a stationary cylinderadapted to be immersed in water and having a front end which is closedand a rear end which is open, a piston slidingly carried in thecylinder, means for locking the piston in position near the rear end ofthe cylinder, a movable system including a plate extending outside thefront end of the cylinder perpensaid plate and slidingly extendingthrough the closed front end of the cylinder, means urging the platetowards the outer surface of the closed front end of the cylinder andthe rod to a projecting position within the cylinder, means adapted torelease the piston locking means whereby the hydrostatic pressureforceably urges the piston forwardly to make it impinge on the rear endof said rod and cause the plateto move outwardly thereby to producesurges in the water, and a bellows interconnecting the outer edges ofthe front end of the cylinder and of the plate to form a closed chamberbetween said front end and said plate.

2. A generator of wave trains in water comprising a stationarycylinderadapted to be immersed in water and having a front end which isclosed and a rear end which is open, a piston slidingly carried in thecylinder,

means for locking the piston in position near the rear end of thecylinder, a movable system including a plate extending outside the frontend of the cylinder perpen-' dicularly to the axis of the latter and arod rigid with said plate and slidingly extending through the closedfront end of the cylinder, means urging the plate towards the outersurface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the plate to move outwardly thereby to produce surges in thewater,and a cylindrical section rigid with the outer edge of the platedirected rearwardly to sealingly and slidingly engage the outerperiphery of the cylinder.

3. A generator of wave trains in water comprising a stationary cylinderadapted to be immersed in water and having a front end which is closedand a rear end which is open, a piston slidingly carried in thecylinder, means for locking the piston in position near the rear end ofthe cylinder, a movable system including a plate extending outside thefront end of the cylinder perpen dicularly to the axis of the latter anda rod rigid with said plate and slidingly extending through the closedfront end of the cylinder, means urging the plate towards the outersurface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the: plate to move outwardly thereby to produce surges in thewater, and a forwardly open cylindrical extension of the cylinder lyingto the front thereof and in which the plate is slidingly and sealinglyfitted.

4. A generator of wave trains in water comprising a stationary cylinderadapted to be immersed in water and having a front end which is closedand a rear end which is open, a piston in position :near the rear end ofthe cylinder, a movable system including a plate extending outside thefront end of the cylinder perpendicularly to the axis of the latter anda rod rigid with said plate and slidingly extending through the closedfront end of the cylinder, means urging the plate towards the outersurface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the plate to move outwardly thereby to produce surges in thewater, and a stationary auxiliary cylinder coaxially rigid with thefirst-mentioned cylinder closed at its outer end and a cylindricalsection coaxially rigid with the plate, extending to the front thereofand adapted to slidingly and sealingly engage said auxiliary cylinder.

5. A generator of wave trains as claimed in claim 4, wherein the plateis constituted by a circular disc.

6. A generator of wave trains as claimed in claim 4 comprising meansfeeding a compressed gas into the cylinderto urge the piston back intoits position near the rear end of the cylinder and means adapted toproduce a partial vacuum to the front of the piston after return of thepiston into said position.

7. A generator of wave trains as claimed in claim 4 comprising hydraulicmeans adapted to control the return of the piston after operation intoits position near the rear end of the cylinder.

1: x s v

1. A generator of wave trains in water comprising a stationary cylinderadapted to be immersed in water and having a front end which is closedand a rear end which is open, a piston slidingly carried in thecylinder, means for locking the piston in position near the rear end ofthe cylinder, a movable system including a plate extending outside thefront end of the cylinder perpendicularly to the axis of the latter anda rod rigid with said plate and slidingly extending through the closedfront end of the cylinder, means urging the plate towards the outersurface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the plate to move outwardly thereby to produce surges in thewater, and a bellows interconnecting the outer edges of the front end ofthe cylinder and of the plate to form a closed chamber between saidfront end and said plate.
 2. A generator of wave trains in watercomprising a stationary cylinder adapted to be immersed in water andhaving a front end whicH is closed and a rear end which is open, apiston slidingly carried in the cylinder, means for locking the pistonin position near the rear end of the cylinder, a movable systemincluding a plate extending outside the front end of the cylinderperpendicularly to the axis of the latter and a rod rigid with saidplate and slidingly extending through the closed front end of thecylinder, means urging the plate towards the outer surface of the closedfront end of the cylinder and the rod to a projecting position withinthe cylinder, means adapted to release the piston locking means wherebythe hydrostatic pressure forceably urges the piston forwardly to make itimpinge on the rear end of said rod and cause the plate to moveoutwardly thereby to produce surges in the water, and a cylindricalsection rigid with the outer edge of the plate directed rearwardly tosealingly and slidingly engage the outer periphery of the cylinder.
 3. Agenerator of wave trains in water comprising a stationary cylinderadapted to be immersed in water and having a front end which is closedand a rear end which is open, a piston slidingly carried in thecylinder, means for locking the piston in position near the rear end ofthe cylinder, a movable system including a plate extending outside thefront end of the cylinder perpendicularly to the axis of the latter anda rod rigid with said plate and slidingly extending through the closedfront end of the cylinder, means urging the plate towards the outersurface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the plate to move outwardly thereby to produce surges in thewater, and a forwardly open cylindrical extension of the cylinder lyingto the front thereof and in which the plate is slidingly and sealinglyfitted.
 4. A generator of wave trains in water comprising a stationarycylinder adapted to be immersed in water and having a front end which isclosed and a rear end which is open, a piston in position near the rearend of the cylinder, a movable system including a plate extendingoutside the front end of the cylinder perpendicularly to the axis of thelatter and a rod rigid with said plate and slidingly extending throughthe closed front end of the cylinder, means urging the plate towards theouter surface of the closed front end of the cylinder and the rod to aprojecting position within the cylinder, means adapted to release thepiston locking means whereby the hydrostatic pressure forceably urgesthe piston forwardly to make it impinge on the rear end of said rod andcause the plate to move outwardly thereby to produce surges in thewater, and a stationary auxiliary cylinder coaxially rigid with thefirst-mentioned cylinder closed at its outer end and a cylindricalsection coaxially rigid with the plate, extending to the front thereofand adapted to slidingly and sealingly engage said auxiliary cylinder.5. A generator of wave trains as claimed in claim 4, wherein the plateis constituted by a circular disc.
 6. A generator of wave trains asclaimed in claim 4 comprising means feeding a compressed gas into thecylinder to urge the piston back into its position near the rear end ofthe cylinder and means adapted to produce a partial vacuum to the frontof the piston after return of the piston into said position.
 7. Agenerator of wave trains as claimed in claim 4 comprising hydraulicmeans adapted to control the return of the piston after operation intoits position near the rear end of the cylinder.